Prior to Target 16.3.1 (March 2016),
Target required a call to
mbox.js to create the global mbox
required for
Adobe Target
to deliver
Target activities, track clicks, and track
most success metrics. This file contains the libraries needed for all of your
activities. You do not need to maintain different activity-specific versions of
the file.

If you already have wrapping mboxes on your pages from an
older style of
Target
implementation, these mboxes can still be used in
the new interface. The updated
mbox.js file is still required, but
these mboxes can be selected for activities and edited using the
Visual Experience Composer.

Target Standard and Premium update and
supplement
mbox.js with a reference to a
target.js file. The
target.js file is hosted by Adobe. The
Target.js file makes it possible to edit
content on any page using the
Visual Experience Composer, even if the
page does not contain predefined mboxes. You must reference this file on every
page on your site.

Although
at.js replaces
mbox.js,
mbox.js will continue to be supported.

Note:Target requires a minimum version of
mbox.js. For more information, see
Target Requirements.

Impact of at.js and mbox.js on Page-Load Time

Many customers and consultants want to know the impact of
at.js and
mbox.js on page-load time, especially in the
context of new vs returning users. Unfortunately, it's hard to measure and give
concrete numbers regarding how
at.js or
mbox.js influence page-load time due to each
customer's implementation.

However, if the Visitor API is present on the page, we can better
understand how
at.js and
mbox.js influence page-load time.

Note: The Visitor API and
at.js or
mbox.js have an impact on page-load time only
when you are using the global mbox (because of the body-hiding technique).
Regional mboxes are not impacted by Visitor API integration.

The following table describes the sequence of actions for new and
returning visitors:

Library Reference

Description

New Visitors

The Visitor API is loaded, parsed, and executed.

at.js /
mbox.js is loaded, parsed, and
executed.

If global mbox auto-create is enabled, the Target
JavaScript library:

Instantiates the Visitor object.

The Target library tries to retrieve Marketing Cloud
Visitor ID data.

Because this is a new visitor, the Visitor API fires
a cross-domain request to
demdex.net.

After Marketing Cloud Visitor ID data is retrieved,
a request to Target is fired.

Returning Visitors

The Visitor API is loaded, parsed, and executed.

at.js /
mbox.js is loaded, parsed, and
executed.

If global mbox auto-create is enabled, the Target
JavaScript library:

Instantiates the Visitor object.

The Target library tries to retrieve Marketing Cloud
Visitor ID data.

The Visitor API retrieves data from cookies.

After Marketing Cloud Visitor ID data is retrieved,
a request to Target is fired.

For new visitors, when the Visitor API is present, Target has to go
over the wire multiple times to make sure that Target requests contain
Marketing Cloud Visitor ID data. For returning visitors, Target goes over the
wire only to Target to retrieve the personalized content.